(covers information from several alternate timelines)
This page contains information regarding Star Trek: Strange New Worlds, and thus may contain spoilers.
He wrote sci-fi and fantasy stories. One of his books was The Kingdom of Elysian. In 2259, Doctor Joseph M'Benga often read this storybook to his daughter Rukiya, who was terminally ill with cygnokemia and forced to stay in the sickbay's transporter buffer for the majority of her life so as to slow-down the progression of the disease. (SNW: "Ghosts of Illyria", "Lift Us Where Suffering Cannot Reach")
When the USS Enterprise was on a survey mission in the Jonisian Nebula, a non-corporeal entity transformed the crew into characters from Benny Russell's story. They all believed that the ship was actually the Kingdom of Elysian, and that the nebula outside was a "smoky wall," made of poisonous air that surrounded their kingdom. The only people unaffected by the transformation was Doctor M'Benga and chief engineer Hemmer. They did find themselves wearing ren faire style clothing, but they still had their minds, unlike the rest of the crew, who were clearly experiencing mind control. It was eventually learned that the entity had learned about the Benny Russell story from the mind of M'Benga's daughter, whom he later found in his quarters and told her they needed to return the crew to normal. (SNW: "The Elysian Kingdom")
In Sisko's visions, Benny was an American science fiction author and ex-naval serviceman living in 1950s New York City who wrote in the Incredible Tales magazine. The editor, Douglas Pabst, and the owner of the magazine were reluctant to reveal that Russell was African-American, at a time when racism was more prevalent in the United States of America. His greatest work "Deep Space Nine" chronicled the adventures of a black captain who commands a space station, a work which was based on a drawing by Roy Ritterhouse.
Benny was determined to see the story published despite the opposition to its subject and the racial identity of its author. Benny's friends, including his fiancée Cassie and friend Willie Hawkins and especially Jimmy, believed he was wasting his time because white society would not accept or read stories by a black American author of science fiction. Russell cited the works of other influential African-American authors of the time, such as Richard Wright, as evidence that the occasional black voice would be heard. (DS9: "Far Beyond the Stars")
Even so, his story was never published and the terrible disappointment, as well as a physical assault, led to his eventual commitment to a psychiatric hospital for treatment for a delusional breakdown. In Sisko's mind, the Pah-wraiths tried to deter him from opening the Orb of the Emissary by making him think that Sisko was Benny, writing out his actions on his room walls. Dr. Wykoff tried to have him paint over the writings, making Sisko bury the Orb. Ezri Dax was able to remind Sisko of his promise to Jadzia as Benny finished the story, opening the box. (DS9: "Shadows and Symbols")
Benny Russell, like Ben Sisko, was played by actor Avery Brooks.
Originally, the main character of "Far Beyond the Stars" would have been Jake Sisko, rather than Ben Sisko, and the episode would have featured a different rationale to account for him being a science fiction writer in the 1950s. (Cinefantastique, Vol. 30, No. 12, p. 62) It was Ira Steven Behr who decided the episode's main character would be changed to Ben Sisko. "As I was driving home, the whole racism thing kind of got to me. It was really one of those moments that didn't happen a lot, but every now and then going home or in a moment when my head was clear, something would just sync up and I'd get all excited. Suddenly it all became Sisko, and he'd be the guy who couldn't get published, because he was an African American," Behr reflected. "And the notion that you are both the dream and the dreamer – it just seemed very cool [....] To an extent it's like shooting ducks in a barrel, because who the hell is going to say that racism is good at this stage of the game? So you're kind of preaching – you would imagine – to the converted already, but I thought it was an interesting way to do it." Behr took his character concept to Avery Brooks. "This idea of this brown man writing, or projecting, this vision of science fiction. I thought that was incredibly clever," Brooks commented. "In addition, [...] that statement made to Sisko: 'You are the dreamer and the dream.' What an incredible notion that is. That's at any time, isn't it? Any epoch, any era. Now, later, yesterday." (The Fifty-Year Mission: The Next 25 Years, pp. 525 & 526) Ultimately, Marc Scott Zicree based the character of Benny Russell on a lot of research, such as Harlan Ellison telling him about a particular man. Zicree later explained, "Harlan told me of a successful '50s author (not in science fiction) who hid behind a white pseudonym until he was 'outed' and his career was ruined [....] I also drew some details of Benny's life from Samuel R. Delany, one of my teachers at the Clarion Writers Workshop." (Cinefantastique, Vol. 30, No. 12, p. 62)
Avery Brooks commented: "Here is a science fiction writer who is brown in 1953. That’s very close to us, you see. When you look at it, you have to think about Samuel Delany and Octavia Butler". 
Actor Jeffrey Combs was highly impressed by the portrayal of Benny Russell in "Far Beyond the Stars". "Avery [...] did some incredible work in front of the camera," Combs enthused. "The end when he breaks down, to me, was just riveting, and so fresh and spontaneous and sincere." (Cinefantastique, Vol. 30, No. 9/10, p. 68) Combs also remarked, "Avery was spectacular. There was a scene toward the end where he falls apart with the camera right in front of his nose. It was just riveting." (Star Trek: Deep Space Nine Companion (p. 537))
Actress Nana Visitor felt likewise, regarding "how on-the-edge Avery [Brooks'] performance was," as she phrased it. She went on to say, "When his character collapses, I remember being alarmed and unsure that the actor was OK. I'd never gotten scared like that for another actor's welfare in all my experience. It was chilling to watch."  
Armin Shimerman was also impressed by Avery Brooks' performance. "I especially remember Avery giving an Emmy-deserving performance as he broke down over the crushing of Ben's dreams. I had tears in my eyes as I watched off camera," Shimerman admitted. "I know many of the Niner fans did the same." 
There was some talk that the final scene of "What You Leave Behind" would feature Benny Russell sitting outside a sound stage holding a script that read "Star Trek: Deep Space Nine", essentially making the series, and all of Star Trek, a dream. (Cinefantastique, Vol. 32, Nos. 4/5, p. 99) Hans Beimler commented, "At one point we were considering ending the series with Benny Russell walking the station, what he imagined. But Benny Russell was something that was introduced in the sixth season. It's important that this series be a seven-year arc, not a two-year arc, so to end on that note I think would have been inappropriate. It's an interesting way to go, [though]." (Cinefantastique, Vol. 32, Nos. 4/5, p. 86) Recalled Ira Steven Behr, "At one point I pitched the idea that at the end of the series everything would have been from the imagination of Benny Russell. Of course they wouldn't let me do that – it would have taken away the entire franchise. But what's so crazy about the idea that DS9 was part of Benny's mind? It's part of Rick Berman's mind and Michael Piller's mind and my mind, Robert [Hewitt Wolfe]'s mind, Hans [Beimler]' mind, René [Echevarria]'s mind, and Ron [D. Moore]'s mind. So of course it's part of someone's mind." (The Fifty-Year Mission: The Next 25 Years, p. 526)
Jerome Bixby – a real science fiction writer to whom a later Star Trek: Deep Space Nine episode entitled "The Emperor's New Cloak" was dedicated (the mirror universe where that the episode takes place was introduced in "Mirror, Mirror", one of four TOS episodes which he wrote) – reportedly used the pen names "Albert Russell" and "J. Russell".
The authors of the Star Trek Encyclopedia (4th ed., vol. 2, p. 243) thought Benny Russell "may have existed in an alternate reality, or perhaps only in certain reaches of Ben Sisko's mind." SNW: "The Elysian Kingdom" confirmed that a real Benny Russell did actually also exist.
In the Deep Space Nine Millennium book trilogy, the Pah-wraiths play off Sisko's fears that Benny Russell is real and that he himself is imaginary, by trapping Sisko in a Pah-Wraith hell where he is given visions that Benny is sitting in his Harlem apartment writing about Benjamin Sisko's adventures.
In the novel Unity, Elias Vaughn has an Orb experience in which he becomes part of the Benny Russell setting; Sisko's communication with the Prophets is portrayed as Benny becoming a "trustee" at the psychiatric hospital from the Pah-Wraith's vision.
In the novel Raise the Dawn, Kira Nerys experiences a vision where Kay Eaton helps Cassie to rescue Benny after he is transferred to prison, the vision inspiring Kira to help Sisko during a later crisis.
In the Crucible novel Provenance of Shadows, Leonard McCoy is stranded in a past alternate timeline following the events of TOS: "The City on the Edge of Forever". A doctor in a South Carolina town, McCoy rescues a drifter science-fiction writer named Benny from some of the racist townsfolk and cares for him in his office.